This invention relates to a charging system for batteries, and more particularly, a charging system for batteries used in power tools. Charging systems for rechargeable power tools generally charge until the battery is fully charged. Often, a user will operate a power tool powered by a lithium ion battery and the battery pack may run out of charge before the work is finished. When this happens, the user may not need a fully charged battery to complete the task, and may only need a battery with a fraction (such as A % of the full battery capacity) of the full capacity to finish the remaining work. For example, a user may require a charging mode for a charger able to charge the battery to 25% capacity within a very short time B, like 3 minutes. Currently, quick-charging chargers available in the market for lithium ion batteries have a very high design cost and have poor mode selectivity and cannot charge the battery to a certain amount to allow a user to finish a certain amount of work in a very short time.